US9451368B2 - Feedback scan for hearing aid - Google Patents
Feedback scan for hearing aid Download PDFInfo
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- US9451368B2 US9451368B2 US13/444,262 US201213444262A US9451368B2 US 9451368 B2 US9451368 B2 US 9451368B2 US 201213444262 A US201213444262 A US 201213444262A US 9451368 B2 US9451368 B2 US 9451368B2
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- 238000012360 testing method Methods 0.000 claims abstract description 37
- 210000003484 anatomy Anatomy 0.000 claims abstract description 16
- 230000004044 response Effects 0.000 claims abstract description 4
- 230000010355 oscillation Effects 0.000 claims description 16
- 238000012545 processing Methods 0.000 claims description 16
- 210000000959 ear middle Anatomy 0.000 claims description 6
- 230000010363 phase shift Effects 0.000 claims description 6
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- 229920000535 Tan II Polymers 0.000 claims description 5
- 230000006870 function Effects 0.000 abstract description 8
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Images
Classifications
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
- H04R25/00—Deaf-aid sets, i.e. electro-acoustic or electro-mechanical hearing aids; Electric tinnitus maskers providing an auditory perception
- H04R25/30—Monitoring or testing of hearing aids, e.g. functioning, settings, battery power
- H04R25/305—Self-monitoring or self-testing
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
- H04R25/00—Deaf-aid sets, i.e. electro-acoustic or electro-mechanical hearing aids; Electric tinnitus maskers providing an auditory perception
- H04R25/45—Prevention of acoustic reaction, i.e. acoustic oscillatory feedback
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
- H04R25/00—Deaf-aid sets, i.e. electro-acoustic or electro-mechanical hearing aids; Electric tinnitus maskers providing an auditory perception
- H04R25/30—Monitoring or testing of hearing aids, e.g. functioning, settings, battery power
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
- H04R25/00—Deaf-aid sets, i.e. electro-acoustic or electro-mechanical hearing aids; Electric tinnitus maskers providing an auditory perception
- H04R25/70—Adaptation of deaf aid to hearing loss, e.g. initial electronic fitting
Definitions
- the present invention pertains to hearing aids, and methods for manufacturing and using such hearing aids.
- Hearing restoration or compensation devices commonly known as hearing aids, provide a tremendous benefit to a patient with congenital hearing loss or whose hearing has deteriorated due to age, genetics, illness, or injury.
- hearing aids There is a wide variety of commercially available devices that can be worn externally or can be implanted within the body of the patient.
- the device In general, it is desirable to provide a high level of gain in the device, so that ambient sound may be significantly amplified for the patient. However, if the gain is too high, some sound may leak from the output speaker to the input microphone, and the device may produce acoustic feedback. Acoustic feedback is a highly undesirable condition, and can lead to a loud squealing noise heard by the patient.
- the characterization may be repeated over an extended period of time, and may help diagnose tissue growth or fluid in the middle ear.
- An embodiment is a hearing aid, including: a sensor that receives ambient sound from around a patient; and a driver that stimulates the anatomy of the patient.
- the hearing aid has an operational mode in which the driver stimulates the anatomy of the patient in response to the sound received at the sensor.
- the hearing aid has a test mode in which a test frequency is stepped through a predetermined range of frequencies. At each test frequency, the driver is driven with a sinusoidal driver signal at the test frequency, the sensor detects a sinusoidal sensor signal at the test frequency, and a comparison of the sensor signal to the driver signal produces an amplitude and a phase for the test frequency.
- Another embodiment is a device for restoring the hearing of a patient, including: a sensor for converting ambient sound around the patient into a corresponding input electrical signal; an audio processing unit for receiving the input electrical signal and producing an output electric signal; and a driver for converting the output electrical signal into a stimulation signal that can be received by the anatomy of the patient.
- the audio processing unit includes a test mode during which the audio processing unit drives the driver with a sinusoidal driver signal at a predetermined frequency, receives through the sensor a sinusoidal sensor signal at the predetermined frequency, compares the sensor signal to the driver signal, and determines a feedback gain and a feedback phase shift at the predetermined frequency from the compared driver and sensor signals.
- a further embodiment is a device for restoring the hearing of a patient, comprising: a sensor for converting ambient sound around the patient into a corresponding input electrical signal; an audio processing unit for receiving the input electrical signal and producing an output electric signal; and a driver for converting the output electrical signal into a stimulation signal that can be received by the anatomy of the patient.
- the audio processing unit includes a test mode during which the audio processing unit drives the driver with a sinusoidal driver signal at a predetermined frequency, receives through the sensor a sinusoidal sensor signal at the predetermined frequency, and samples and stores at least four voltage levels each for the sensor and driver signals. The voltage levels are sampled at intervals that are spaced apart by one-fourth of an oscillation period at the predetermined frequency.
- FIG. 1 is a block diagram of an implantable hearing restoration device
- FIG. 2 is a schematic drawing of a sample implantable hearing restoration device
- FIG. 3 is a flow chart of the method of operation for the device of FIG. 2 ;
- FIG. 4 is a plot of the driver signal voltage (top) and the sensor signal voltage (bottom) versus time.
- hearing aid is intended to mean any instrument or device designed for or represented as aiding, improving or compensating for defective human hearing and any parts, attachments or accessories of such an instrument or device.
- a hearing aid having the ability to generate its own open-loop feedback scan of amplitude (as gain or attenuation) and phase, as a function of frequency.
- the hearing aid has a sensor that receives ambient sound from near a patient, and a driver that stimulates the anatomy of the patient.
- the hearing aid has an operational mode in which the driver stimulates the anatomy of the patient in response to the sound received at the sensor.
- the hearing aid has a test mode in which a test frequency is stepped through a predetermined range of frequencies.
- the driver is driven with a sinusoidal driver signal at the test frequency
- the sensor detects a sinusoidal sensor signal at the test frequency
- a comparison of the sensor signal to the driver signal produces an amplitude (gain or attenuation) and a phase for the test frequency.
- FIG. 1 is a block diagram of an implantable hearing restoration device 1 , with arrows that trace the flow of acoustic signals.
- the acoustic signals flow from a sound environment 2 , to an implantable hearing restoration device 1 , to a patient anatomy 6 .
- the sound environment 2 may be the acoustic environment in which the patient and hearing device 1 exist, such as a quiet office, a busy street, or a soundproof booth that may be used for audiometric testing.
- the sound environment 2 may create sounds that are within the typical pressure and frequency range that a human with normal hearing can perceive. In general, a typical frequency range for normal human hearing may be between 20 Hz and 20 kHz, although the high-frequency edge of this range typically decreases with age. Note that the sound environment 2 may produce acoustic signals outside the frequency range of human hearing as well, although the implantable hearing restoration device 1 may be largely unaffected by these signals. Sounds produced by the sound environment 2 arrive at the implantable hearing restoration device 1 in the form of acoustic pressure waves.
- the implantable hearing restoration device 1 may include three general units, including a sensor 3 or microphone 3 , a processor 4 or amplifier 4 , and a driver 5 or electrode 5 .
- the driver 5 or electrode 5 may also be referred to as a speaker.
- the sensor 3 may be an element or transducer that converts mechanical or acoustic energy into an electrical signal, such as a microphone or piezoelectric sensor.
- the sensor 3 receives the sound produced by the sound environment 2 and converts it into an input electrical signal.
- the input electrical signal may be generated in a known manner.
- the processor 4 processes the input electrical signal from the sensor 3 , and may amplify, filter and/or apply other linear and/or non-linear algorithms to the input electrical signal.
- the processor 4 produces an output electrical signal and sends it to the driver 5 .
- much of the remainder of this document is directed to particular processing performed by the processor 4 , and there is much more detail concerning the processor 4 in the text that follows.
- the driver 5 receives the output electrical signal from the processor 4 and converts it into a stimulation signal that can be received by the patient anatomy 6 .
- the stimulation signal may be acoustic, mechanical and/or electrical in nature. For the purposes of this document, it is assumed that the stimulation signal may be received in a known manner.
- the implantable hearing restoration device 1 can characterize the feedback network between the driver 5 and the sensor 3 . Specifically, the implantable hearing restoration device 1 may characterize the relationship between the input electrical signal received from the sensor 3 and the output electrical signal sent to the driver 5 . If there is sufficiently high gain between the input and output electrical signals, then there may be conditions at which the device 1 can produce undesirable feedback. A device said to be “in feedback” may be unstable and may be in oscillation, usually at one particular frequency. Feedback in a hearing aid is highly undesirable.
- the physical cause of feedback may vary, depending on the type of hearing aid.
- feedback may be caused by acoustic energy leaking back from the output speaker to the input microphone and consequently being amplified repeatedly. This causes the amplifier or processor to oscillate and causes the patient to hear a loud squealing noise.
- feedback may be caused by vibrations coupling back into the sensor through bone in the patient's head, through fluid residing in the middle ear, and/or tissue that has grown since the device was implanted.
- Characterization of the feedback network may provide the clinician with a value of the maximum gain that the device 1 could provide before feedback or oscillation occurs. In general, such a value is beneficial, in that it allows the clinician to increase the gain as much as possible without risking feedback. In addition, if such a characterization were repeated over time, a clinician could use the results over time to help diagnose physiological changes such as tissue growth or fluid in the middle ear.
- FIG. 2 is a schematic drawing of a sample implantable hearing restoration device 1 .
- the sample device 1 shows particular modules and elements that perform particular functions. It will be understood by one of ordinary skill in the art that the configuration of FIG. 2 is merely an example, and that other modules and elements may be used to perform the particular functions noted in detail below.
- the sensor 3 and the driver 5 are shown in the example of FIG. 2 as being electrically capacitive in nature, it will be understood that other sensors and drivers may be used that need not be based on capacitance.
- the sensor 3 electrically connects to the processor 4 through a transducer connection 18 .
- the electrical signal produced by the sensor 3 enters an input amplifier 13 .
- the signal from the input amplifier 13 enters an audio processor 16
- the signal from the audio processor 16 feeds an output amplifier 14 , which in turn connects electrically through a transducer connection 19 to the driver 5 .
- the day-to-day operation of the device 1 may use all-analog processing of the sound, rather than conversion to digital, processing in the digital domain, and conversion back to analog.
- the input amplifier 13 , the audio processor 16 and the output amplifier 14 may be grouped collectively as an audio processing unit 11 , although the individual components need not be physically grouped together in the same location on a circuit board or integrated circuit.
- the processor 4 includes a set of digital diagnostic controls 12 that can control the analog elements, and can control properties such as the gain, equalization, compression/limiting, and so forth.
- Two additional components that may be used to analyze the feedback network are a signal generator 15 and a sampler/analog-to-digital converter 17 , both of which may be grouped with the audio processing unit 11 .
- the signal generator 15 may generate a sine wave of a known frequency and amplitude. The frequency and amplitude may be controlled by the digital diagnostic controls 12 .
- the sinusoidal output from the signal generator 15 may be fed into the output amplifier 14 , which in turn, drives the driver 5 .
- the driver 5 stimulates the anatomy of the patient, and a small portion of the sinusoidal energy may be picked up by the sensor 3 .
- the sinusoidal signal received by the sensor 3 may be amplified by the input amplifier 13 .
- the output from the input amplifier 13 may also feed the sampler/analog-to-digital converter 17 , in addition to feeding the audio processor 16 .
- the sampler/analog-to-digital converter 17 may sense an amplitude and a phase for the sinusoidal signal, and may store the sensed amplitude and phase in memory within the audio processing unit 11 or external to the audio processing unit 11 .
- the digital diagnostic controls may then change the sine wave frequency of the signal generator 15 , and the process may repeat. The process is then repeated with sufficient resolution in frequency, over a sufficiently large range of frequencies, resulting in the device having acquired a set of measured amplitudes and phases as a function of frequency.
- FIG. 3 is an example flow chart of the method of operation 20 for the device 1 of FIG. 2 .
- the signal generator 15 generates an electrical sine wave of a predetermined frequency.
- the signal generator 15 directs the electrical sine wave to both the output amplifier 14 and the sampler/analog-to-digital converter 17 .
- the output amplifier 14 amplifies the electrical sine wave while blocking all other inputs to output amplifier 14 .
- the output amplifier 14 directs the amplified electrical sine wave to the driver 5 . Upon leaving the driver 5 , the sine wave propagates as sinusoidal acoustic energy within the anatomy of the patient.
- the sensor 3 receives the sinusoidal acoustic energy propagating within the anatomy of the patient.
- the sensor 3 generates a received electrical signal from the received sinusoidal acoustic energy and directs it to the input amplifier 13 .
- the input amplifier 13 directs the amplified received electric signal to the sampler/analog-to-digital converter 17 .
- the amplified received electric signal is compared to the electrical sine wave.
- the amplitude and phase are extracted.
- step 30 the signal generator 15 adjusts the frequency of the electrical sine wave, and, optionally, the amplitude of the electrical sine wave as well. In some cases, the increment of frequency is predetermined to have sufficient resolution in the frequency domain. Steps 21 - 29 are then repeated until the full frequency range is covered.
- the device 1 may instead store several sampled values from the electrical sine wave and the amplified received electrical signal, the samples being taken at predetermined times. Once all the frequencies are swept, the device may then use all the stored sample values to determine the amplitude and phase at each frequency. In other words, the amplitude and phase may be calculated for each frequency as the data is taken, as is drawn in FIG. 3 , or may alternatively be calculated all at once after all the data has been taken. In some cases, the stored values may be exported to a separate device, such as a module external to the patient, and the amplitudes and phases are calculated from the stored values on said external device or another external device.
- the sampler/analog-to-digital converter 17 It is instructive to work through some numbers, which may serve as rough guidelines for the requirements on the sampler/analog-to-digital converter 17 .
- Typical patients having moderate to severe hearing loss may have hearing thresholds of up to 70 dB to 95 dB below that of someone with normal hearing.
- the hearing devices designed to treat moderate to severe hearing loss should be capable of providing 70 dB to 95 dB of gain.
- the feedback network should have a gain of no more than ⁇ 95 dB, or the device will go into oscillation (i.e. feedback) before reaching maximum gain. Therefore, the sampler/analog-to-digital converter 17 should be able to resolve signals that are about 100 dB quieter than that of the test signal being output by the driver 5 .
- the feedback characterization may have high precision over a large dynamic range, may capture both magnitude and phase information, and may be performed quickly to minimize time for the patient and the clinician.
- the signal generator 15 may begin outputting a sine wave with the selected frequency and amplitude. After a short time, typically a few oscillation periods, the signal generator 15 has settled into a steady-state oscillation having a relatively stable amplitude and being relatively free from transients.
- the value of the frequency is fed to the sampler/analog-to-digital converter 17 , so that the sampler/analog-to-digital converter 17 may sample signal values at specific time intervals that depend on the frequency. Specifically, for each frequency, the sampler/analog-to-digital converter 17 samples four values from both the signal generator 15 (representing the driver signal) and the input amplifier 13 (representing the sensor signal). The four values are taken at intervals of 90° of phase, or one-fourth of a full rotational period or cycle. The driver signal and the sensor signal are sampled at the same time.
- FIG. 4 is an example plot of the driver signal voltage (top) and the sensor signal voltage (bottom) versus time.
- the period of both oscillatory voltages is denoted as “P”, which mathematically is the inverse of the oscillation frequency.
- P phase shift between the driver and sensor signals
- There is a phase shift between the driver and sensor signals which is one of the quantities to be calculated.
- There is a peak-to-valley voltage of the driver signal denoted as “2AC D ”, which is an intermediate quantity to be calculated.
- the peak-to-valley voltage is an AC component to the voltage; there is also a DC offset to the voltage not shown explicitly in FIG. 4 .
- the peak-to-valley voltage of the sensor signal is denoted as “2AC S ”, which is also an intermediate quantity to be calculated.
- the gain of the system is one of the useful quantities to be calculated, and is given by the ratio of 2AC S /2AC D .
- the four time values are designated as “1”, “2”, “3” and “4”, the driver signal is designated as “D”, and the sensor signal is designated as “S”.
- the four measured driver signal voltages are then “D 1 ”, “D 2 ”, “D 3 ” and “D 4 ”, and the four measured sensor signal voltages are then “S 1 ”, “S 2 ”, “S 3 ” and “S 4 ”.
- D 1 and S 1 are measured at same instant
- D 2 and S 2 are measured at the same instant one-fourth of a period after D 1 and S 1 , and so forth.
- the device 1 captures a total of eight signal voltages: D 1 , D 2 , D 3 , D 4 , S 1 , S 2 , S 3 and S 4 .
- the gain (or attenuation) may also be expressed in decibels, by taking 20 log 10 of the above quantity.
- phase in units of time may be found by multiplying the value in radians by the oscillation period P and dividing by 2 ⁇ .
- sampling times “1”, “2”, “3” and “4” need not be simultaneous for both the driver and sensor signals, since true simultaneity may be difficult for the sampler/analog-to-digital converter 17 .
- the sampling times may be offset by a known amount, such as a fixed time delay or a fixed portion of a rotation period.
- the term “simultaneous” is intended to cover both true simultaneity, and the cases where the sampling times are offset by a known, predetermined amount.
- the period of oscillation is one divided by the oscillation frequency.
- the driver and sensor signals are simultaneously sampled at four instances, the instances being regularly spaced apart by one-fourth of an oscillation period.
- the sampled signals total eight sampled voltages.
- the gain and phase shift of the system are extracted through straightforward formulas from the eight sampled voltages.
- the process may be repeated over a range of frequencies, where the range may include the full range or a partial range of human hearing. This produces the gain and phase shift of the system, versus frequency, over a desired range of frequencies.
- the measurement can be very fast, requiring at most only a few periods of oscillation for each frequency. For a reasonable scan of the full range of human hearing, a full measurement may only take perhaps two or three seconds.
- the measured quantities require very little memory, merely eight stored voltage values for each frequency.
- the equations for extracting the amplitude and phase from the eight stored voltage values are robust, and do not include any undefined points at which division by zero occurs or accuracy is compromised.
- the four time instances can start at any absolute time without affecting the results, there is no need for triggering from a particular starting point in the oscillations, such as a peak or a zero-crossing.
- the feedback signal path may be isolated from the forward signal path.
- the measurement requires no additional equipment.
- the measurement technique can be implemented in both externally worn and in fully implantable hearing aids. Additionally, the measurement can be performed while wearing an ear plug to dramatically reduce error due to ambient noise. In addition, the measurement may be performed automatically by the device, and needs no additional calibration. Also, the measurement is not susceptible to variation in test equipment over time. Further, the measurement may be used to detect tissue growth and fluid in the middle ear. Finally, the measurement may be used to detect other issues with fully implantable systems.
Abstract
Description
2AC S=[(S3−S1)2+(S4−S2)2]1/2
2AC D=[(D3−D1)2+(D4−D2)2]1/2
Gain=2AC S/2AC D=[(S3−S1)2+(S4−S2)2]1/2/[(D3−D1)2+(D4−D2)2]1/2
Phase [radians]=a tan 2[(D4−D2), (D3−D1)] a tan 2[(S4−S2), (S3−S1)],
Claims (12)
[(S3−S1)2+(S4−S2)2]1/2/[(D3−D1)2+(D4−D2)2]1/2;
a tan 2[(D4−D2), (D3−D1)]−a tan 2[(S4−S2), (S3−S1)].
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